Vapor/immersion cleaning method for soiled parts

ABSTRACT

An automated open topped apparatus and improved method for cleaning soil from metal parts which employs a low vapor tension, low density, LVTC, liquid cleaner in a first tank and a high vapor tension, higher density, immiscible rinse, HVTR, liquid in a second tank and a rinse vapor zone above both tanks in the apparatus which provides steps and means for preventing rinse vapor loss during shut down periods by using microprocessor controlled steps that cause a layer of the liquid cleaner to be positioned atop and cover the liquid rinse in its tank and at the end of the idle period returns the liquid cleaner cover to the first tank and re-starts the cleaning process and thereafter monitors and controls cleaning operation until the succeeding shut down period.

This is a continuation of application Ser. No. 08/021,423, filed on Feb.23, 1993, now U.S. Pat. No. 5,327,920.

BACKGROUND OF THE INVENTION

This invention relates to vapor/immersion cleaning apparatus of thedegreaser type for removing soils such as greases, waxes or the likefrom metal and other parts which is programmably controlled and amicroprocessor controlled method for eliminating undesirablevaporization of expensive and/or toxic solvents from the open toppedplural-tank cleaning apparatus during periods of shut down, start up,and normal cleaning operation.

Dry cleaning machines and metal degreasing apparatus having an open topand one or more solvent tanks using a single vaporizable solvent such astrichloroethylene or perchloroethylene had been used in the UnitedStates commercially by as early as the mid 1950's. Such apparatus andprocesses for cleaning metal by vapor phase cleaning, or combinations ofvapor phase with immersion cleaning in an agitated solvent, or byagitating the parts while immersed in such solvent, are disclosed inexpired U.S. Pat. Nos. 3,216,431 and 3,593,727. By the mid 1960'sapparatus having water cooled conduits located peripherally on the wallsof open top metal cleaning apparatus for creating a vapor zone above thecleaning liquids and methods for cleaning and for condensing solventvapors and reusing the condensed solvent were being used commercially.Such apparatus and methods are disclosed in U.S. Pat. Nos. 3,227,629,3,610,260 and 3,676,307.

The continuing problem of escape of some quantity of solvent vapors fromsuch apparatus continued into the late 1960's and led to improvement inrecovery processes by distillation such as is disclosed in U.S. Pat. No.3,483,092. By the late 1970's low boiling fluorocarbon solvents, orazeotropes thereof with methylene chloride that boiled below 100° F.,had been developed along with ultrasonic transducers. Commercial use ofthe combination of such solvents with the sonic transducers led to theinvention of a compression-expansion type refrigeration system andapparatus that improved control of solvent vapor zones and decreasedsolvent losses. That apparatus and process is disclosed in U.S. Pat. No.4,055,196, issued Oct. 25, 1977, to Thomas J. Kearney and entitledImmersion Type Metal Degreaser With Compression-Expansion System forHeating and Cooling of Liquid Solvent and Solvent Vapors.

Technical information extant by the mid 1980's that ozone depletion inthe atmosphere is partially attributable to the presence of chlorinemade metal cleaning with chloro-fluoro hydrocarbons less desirable andhas sparked renewed research efforts for identifying and developingsubstitute solvents for cleaning soil from parts. An effective, no-failsystem for eliminating solvent vapor losses in open topped metalcleaning apparatus during shut down times had not been found prior tothe present invention.

SUMMARY OF THE INVENTION

The present invention is directed to automated apparatus and amicroprocessor controlled process that solves the problem of undesirablerelease of expensive, or toxic or ozone-depleting solvent vapors intothe atmosphere resultant from vapor-immersion cleaning in open toppedapparatus of soil from metal, printed circuit boards or other parts, andwhich apparatus and process can be operated and conducted in a safeeconomic, commercially feasible manner.

The automated apparatus of this invention is a modified version of thetype of degreaser disclosed in U.S. Pat. No. 4,055,196 which is owned bythe assignee of the present invention. The new apparatus is similar tothat of the '196 patent in certain respects in that it uses side by sideboil and vapor distillate tanks separated by a common wall, andincorporates an ultrasonic transducer and a refrigeration system forcooling the liquid solvent and the solvent vapors.

The modifications in the new automated apparatus of this invention havebeen added to accommodate a process of metal cleaning using twodifferent liquids in the two tanks that are immiscible, that is, acleaning and rinsing liquid that are chemically dissimilar and which donot dissolve in each other when mixed. The new apparatus adds means totransfer a portion of the immiscible rinse liquid into the cleaningliquid tank by a route, different from the normal cascading route fromthe rinse tank into the boil tank. The procedure employed and the meansadded to the apparatus to make the new method possible to accomplishinclude means which automatically position a covering layer of cleaningliquid of controlled depth over the surface of the liquid in the rinsetank during the shut down period of the cleaning operations. Other meansare added to the apparatus enabling re-transfer of the cover layer ofcleaning liquid from its position atop the rinse liquid back into thecleaning tank. The microprocessor automatically initiates a start up ofthe apparatus, and then monitors and controls the cleaning operationwhich will De more specifically explained in the detailed descriptionhereinafter.

The new process of this invent ion includes new microprocessorcontrolled steps of cover layer formation and removal which preventsloss of the vapor condensate into the atmosphere during shut downperiods of idle time between cleaning operations without requiring theexpensive continued operation of the refrigeration components of theapparatus which is ordinarily required to maintain a vapor zone withinan open topped degreaser to reduce, or avoid, such losses in order tomeet safety requirements. Thus, the new process is cheaper as the resultof savings of expensive solvents and the avoidance of refrigerationcosts during idle periods.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a front elevational view of the open top apparatus inaccordance with this invention;

FIG. 2 is a left side elevational view of the apparatus of FIG. 1;

FIG. 3 is a top plan view of the apparatus of FIG. 1;

FIG. 4 is a simulated front view of the apparatus of FIG. 1 illustratingnormal operating conditions and showing pump and liquid circulation toachieve agitation in both tanks and relative rinse liquid and cleanerliquid levels in tanks 15, 16;

FIG. 5 is a front view similar to FIG. 4 but illustrating the separatedrinse liquid underlying the cleaner liquid after pumping agitation hasceased and shortly after shut down with both pumps off;

FIG. 6 is a front view similar to FIG. 4 illustrating reversal ofsolenoid valve 38 to closed and reversal of solenoid valve 44 to open,and with boil tank pump 43 off, the transfer of rinse liquid from thebottom of the rinse tank to the bottom of the boil tank causes thecleaner liquid to rise in level and cascade into the rinse tank to forma liquid cover to the level sensor pre-set depth;

FIG. 7 is similar to FIG. 4 and illustrates the removal of the coverlayer by raising the rinse level in the rinse tank to cascade thecleaner cover layer over the dam and back into the boil tank to thusready the system for normal cleaning operation when the rinse agitationpump is turned on; and

FIG. 8 is a schematic block diagram of the programmable logic controllercorrelating the apparatus elements controlled, and process stepsinitiated and paramaters monitored and controlled under shut-down,start-up and the various operating modes of the apparatus and process.

BEST MODE FOR CARRYING OUT THE INVENTION

As shown in the drawings, the improved apparatus of this inventionillustrates an open top modified degreaser which comprises a housing ofnon-corrosive metal having continuous, flat front wall 11, rear wall 12,left and right end walls 13 and 14. The interior of housing 10 isseparated into two tanks or chambers, a rinse chamber 15 and a boilchamber 16. The two chambers are separated by a common partition 17terminating at its upper end in a dam 18 sloping upwardly from the rinsechamber 15 toward boil chamber 16, the upper edge surface of whichestablishes the normal level of the rinse liquid during cleaningoperations and is the surface over which that liquid rinse continuouslycascades into the boil chamber as indicated by arrow 19.

A vapor zone 20 within housing 10 extends between the top of the rinseand boil tanks 15, 16 upwardly to a level preferably no higher than halfway up the bank of six primary condenser coils 21, shown in FIG. 1. Asshown in FIGS. 2 and 3, the primary coils 21 extend peripherally on theinterior surface of each wall and surround the entire vapor zone 20.Immediately beneath primary condensor coils 21 is an inwardly extendingtrough 22 which collects the vapor condensates. Each wall surface troughslopes downwardly sufficiently to drain all of the distillates into thewater separator/rinse distillate receiving tank 23. As best seen inFIGS. 4-6, rinse distillate tank 23 is piped to distillate port 24which, during operation, empties the distillate directly into rinse tank15.

This continuously added distillate into tank 15 keeps the rinse liquidat the top level of dam 18 and produces the cascading transfer into boiltank 16. Boiling of the agitated admixture of rinse liquid with thecleaning liquid in tank 16 continuously vaporizes the rinse liquid toform the vapor that occupies vapor phase zone 20, then condenses whencooled and returns to rinse tank 15 as stated.

The sloped bottom 55 of rinse tank 15 supports a plurality of sonicimploders powered by the sonic power assembly 25 which is ofconventional type. Suitable equipment of this type includes fixedfrequency, adjustable frequency and/or square wave type sonic powersources available from Ultrasonc Power Co., Freeport, Ill. or CrestUltrasonics Corp., Trenton, N.J.

Boil chamber 16 contains a work rest support 26 which acts as a supportsurface for baskets of metal or other types of parts being processed inthe liquid cleaning solvent contained in chamber 16. A heating element27 is positioned in chamber 16 beneath work rest support 26 andprotected by cover 28. The temperature of the liquids in boil chamber 16is measured by low temperature thermometer 29 over the range of, forexample, 0°-200° F. and by high temperature thermostat 30, both of whichare electrically connected to the microprocessor 31, not shown, butlocated within housing 36 and graphically depicted in block diagram,FIG. 8.

A programmable logic controller, PLC, having functional capabilitiesincluding counters, sequencers, timers, relay logic and shift registers,and containing a processor, CUP and capacitor-backed CMOS RAM memory,such as is commercially available in the United States fromAllen-Bradley, Milwaukee, Wis. under the designation SLC™ 150Programmable Controller is suitable for use to automate the apparatusand to initiate, monitor, and control the steps of the process of thisinvention.

An overall block diagram is shown in FIG. 8 of the apparatus and processrequests, notifications as to operating parameters monitored andcontrolled, within preset limits, to accomplish the cleaning operationmode as illustrated in FIG. 4; to accomplish the shut-down conditionprior to liquid cover formation and placement of the liquid cover overthe rinse liquid as illustrated in FIG. 5; to accomplish the automaticplacement of liquid cover over the rinse liquid as illustrated in FIG.6, and to accomplish the removal of the liquid cover by replacement ofthe cleaner liquid into the boil chamber 16 and start up as illustratedin FIG. 7.

The portion of the interior of housing 10 above the primary condensercoil bank 21 is provided with two additional sets ofchiller/dehumidification coils which serve, during operation of thecleaning process, to maintain low ambient temperatures in the freeboardzone above the primary coils 21 and thus reduce, and ideally preclude,rinse vapor losses from the open topped apparatus and into theatmosphere. In the illustrated apparatus of FIGS. 1-3, the first doublecoil set of freeboard chilling coils 32 is located immediately above theprimary condenser coils 21 and rinse vapor distillate or ambient airmoisture that condenses on these coils falls into trough 22 and isdischarged into rinse distillate tank 23 through port 24. The second setof chiller/dehumidification coils 33 is located closely adjacent to theopen top 34 of housing 10. Distillates that form on the coils 33 arecollected in trough 35 and transferred through pipes 36 to receivingtank 23 or discarded directly through a waste water exit.

The chiller/dehumidification coil sets 32, 33 normally operate atapproximately -20° F. whereas primary condenser coils 21 normally aremaintained at approximately 40° F. The desired temperatures aremonitored and controlled within pre-set limits by the microprocessor 31,not shown.

Agitation of the rinse solutions in tank 15 is obtained from thecirculation of rinse liquid by pump 37, connected by piping throughsolenoid valve 38, controlled by microprocessor 31 and programmed to benormally open during cleaning operation. Rinse is withdrawn from thebottom area of tank 15 through port 39, and passes through filter 40 anddischarges through spray headers 41 and eductor nozzles 42 angleddownwardly and inwardly to enhance agitation in addition to thatsupplied by the sonic imploders 25. A similar pump and pipingarrangement is used in agitating the cleaning liquid in boil tank 16 andincludes pump 43, withdrawal port 45, filter 46 and injects liquiddownwardly and inwardly into spray headers 47 positioned near the normaloperating level of the cleaning liquid in tank 16.

Due to the immiscibility of the cleaning and rinse liquids used in theprocess of this invention it is important to assure sufficient agitationof the continuously cascading rinse liquid into the cleaning liquid inthe boil chamber to enable efficient vaporization of the rinse to formand maintain the vapor blanket in vapor space 20 overlying both tanks15, 16. As soiled metal parts are lowered through the open top andfreeboard zone into the vapor zone above the tanks, the hot vaporassists soil removal by heating and softening the soil as it approachesthe work rest support 26 upon immersion in the cleaning liquid in boiltank 16. Cleaning during immersion first in the boil tank cleaner andlater upon immersion in the rinse solution is also somewhat assisted bythe agitation within the cleaning and/or rinse liquids.

As indicated above, the improved process of this invention solves theproblem of loss of highly volatile vapor phase materials during shutdown periods in the operation of the open top, two tank metal cleaningapparatus above descirbed. The process applies to solvents referred toabove, generally, as cleaning liquids and rinsing liquids and there arenumerous and varied specific materials in each category. Such materialsresulted from research for non-toxic, non ozone-depleting replacementmaterials for chlorinated hydrocarbons that have been discouraged foruse as cleaning solvents for environmental reasons since about themiddle 1980's.

The preferred process of this invention is concerned with the use ofcleaner and rinse liquids which are immiscible with each other and whichquickly stratify into easily discernible layers readily visible to thenaked eye. The cleaner liquid should be capable of dissolving,dislodging or solvating the soil to be removed. Additionally, the rinseliquid is preferably easily converted from liquid into vapor by heatingan admixture of the rinsing and cleaning liquids by boiling thatadmixture, The rinse, or vapor phase forming component, is typically alow boiling point material that volatilizes easily, and hereinafter, andin the claims, will be identified as a high vapor tension rinse liquid,HVTR liquid. Vapor tension is the tendency of a liquid to form a vaporand high vapor tension as herein used refers to liquids which at roomtemperature and sea level pressure are highly volatilizable and usuallyhave boiling temperatures below about 140° F. The rinse liquid, and orrinse in vapor form, aids in, and serves to remove and clean thesolvated soil from the metal or other part being cleaned of soils whichare typically greases, oils or waxes and may include adhesives, rosinsor rosin fluxes on printed circuit boards.

The process of this invention is specifically concerned with preventingthe loss of the high vapor tension rinse liquid by volatilization atroom temperature from a rinse tank in the apparatus of this inventionduring shut down periods. The process accomplishes that result in twomicroprocessor controlled steps; (1) positioning a cover layer of lowvapor tension cleaner liquid over the upper surface of high vaportension rinse, HVTR liquid in the rinse tank at shut down of thecleaning operation in the apparatus of this invent ion; and (2) removingthe cover layer and re-starting the cleaning operation of the apparatus.

The low vapor tension cleaner material preferably has a substantiallyhigher boiling point than the high vapor tension rinse material, andideally, does not vaporize at all, or to any appreciable degree, at theboiling point, or vaporization temperature, of the rinse material whenthe admixture with the cleaning liquid is boiled. Hereinafter, and inthe claims, the cleaner or cleaning liquid in the boil tank will bereferred to as a low vapor tension cleaner liquid, LVTC liquid. In apreferred embodiment of this invention, illustrated in greater detail inconnection with FIGS. 4-7 hereinbelow, in addition to immiscibility ofthe HVTR and LVTC liquids, it is desirable for the LVTC liquid to have alower density than the HVTR liquid and in selecting particularcombinations it is preferable to select HVTR and LVTC materials having awide difference in density.

The improved method of this invention of preventing loss of high vaportension rinse liquid is not restricted to any specific material, orcombination, or composition but rather is applicable for use with anycombination of cleaner and rinse materials that have been identified inany of numerous prior art patents such as, for example, Hayes et al U.S.Pat. No. 4,640,719 which discloses cleaning rosin solder flux fromprinting wiring boards by using terpene compounds, and Dishart et alU.S. Pat. No. 4,867,800 which discloses using dibasic ester solvents incombination with a terpene compound. Rodgers et al U.S. Pat. No.5,075,982 discloses low boiling point HCFC solvents for use in open topdefluxer apparatus as replacements for the ozone depleting solventsCFC-113 and these HCFC solvents are materials that appear to be includedwithin the category of high vapor tension rinse HVTR liquids suitablefor use with an immiscible low vapor tension cleaner LVTC liquid thatmay include terpenes of the Hayes '719 patent or the combinations of theDishart '800 patent.

The microprocessor controlled steps of the method of this invention canbe best understood in connection with the representation of theconstituent phases of the automated cycle of operation of the apparatusthat is illustrated in FIGS. 4-7 of the drawings that will now beexplained.

FIG. 4 is a schematic front view representation of the apparatus of FIG.1 illustrating the pump and piping layout including the microprocessorcontrolled solenoid valves that functionally enable the automaticplacement of a cover layer of the LVTC liquid over the top surface ofthe HVTR liquid in the rinse tank at shut down of an operating conditioncycle of the apparatus. FIG. 4 shows the HTVR liquid at the level of thetop of dam 18 and cascading over that dam into boil tank 16 as shown byarrow 19. The LVTC liquid level in boil tank 16 is below dam 18,typically approximately 2" below the level of the HVTR liquid.

Agitation of the HVTR liquid is provided by pump 37 which is on andpumping HVTR liquid as shown by the arrows on the simulated piping fromport 39 through filter 40 and HVTR liquid is ejected downwardly andinwardly into the upper portion of the HVTR liquid through spray headers41 and into the mid-portion through eductor nozzles 42, with theagitation within the LVTC liquid being further enhanced by sonicagitation as previously mentioned.

Boil tank agitation results from withdrawal of LVTC liquid through port45 by pump 43, through filter 46 and is discharged through spray headers47. Heating element 27 is on and boiling occurs, typically in the rangemonitored by the microprocessor between 100° F. and 200° F. that isappropriate for the particular LVTC liquid being used.

FIG. 5 is a schematic front view of the apparatus of FIG. 4 at a timeshortly after shut-down has been initiated, the pumps 37, 43 are off andagitation has ceased. The HVTR liquid is at dam 18 level, heat toelement 27 is off and the LVTC liquid in boil tank 16 has cooledsomewhat and stratified above the separated HVTR liquid which is shownbeneath the LVTC liquid.

FIG. 6 illustrates the process step of forming a liquid cover layer ofLVTC liquid over the surface of the HVTR liquid in the rinse tank 15.The formation step is initiated by the microprocessor closing rinse tanksolenoid 38 and opening solenoid 44. Pump 37 is then activated towithdraw HVTR liquid from the bottom port 39 and to transfer that liquidinto the bottom port 50 in boil tank 16 at a rate insufficient toagitate the LVTC strata in tank 16. That transfer is continued undermicroprocessor control until the LVTC liquid is raised to the level ofdam 18 and cascades into tank 15 to form a cover layer 51 to the pre-setlevel of the top level sensor 52 which signals the microprocessor tode-energize pump 37. Thereafter, the refrigeration provided by units 48and 49, shown in FIG. 2, to the primary cooling coils 21, and the freeboard chiller coils 32 and dehumidifier coils 33 stops, aspreprogrammed.

FIG. 7 illustrates the automated steps of the process that occur at theend of the shut down period when a decision to restart the apparatus hasbeen made. The first step is a microprocessor response to a signal fromthe low level limit sensor 53 of the cover layer 51.

That sensor 53 is located at the low level limit of cover layer 51. Itsposition reflects the normal lowering of the cover layer level,approximately 2" due to the decrease in liquid volumes resulting fromcooling from the temperature near boiling at shut-down time to thecooler temperature at start-up time. Such sensor 53 activation of themicroprocessor initiates pump means to supply HVTR liquid make-up froman auxiliary supply tank, not shown, in sufficient quantity toreposition the top surface of the cover layer 51 at the initial level oftop level sensor 52, which then deactivates the pump means and signalsthe microprocessor that start-up steps may be effected.

These start-up steps include de-energizing the cool-down selectorswitch, energizing the main disconnect switch, start refrigeration units48, 49, turn on the boil tank pump 43, turn on heat to element 27. Whenthe admixture of HVTR and LVTC liquids reach boiling, vapor of HVTRfills the vapor zone 20, vapor condenses on primary coils 21, thedistillate flows through distillate tank 23 and empties into rinse tank15. As the quantity of distillate into tank 15 increases, the HVTR levelrises and pushes the cover layer 51 upward and causes it to cascade overdam 18 back into boil tank 16 as indicated by arrow 54. When the layer51 is completely removed and repositioned in tank 16, and HVTR begins tocascade again over dam 18, the microprocessor activates rinse tank pump37 thus re-establishing operating conditions for processing soiled metalparts under the monitoring controls of the microprocessor 31 asdescribed in connection with FIG. 4.

What is claimed is:
 1. A microprocessor controlled cyclical process ofsolvent cleaning soils from parts in an open top apparatus comprising acleaning mode cycle and a shut down cycle, said apparatus having a boiltank containing an agitated admixture of high vapor tension rinse liquidand low vapor tension cleaner liquid and a rinse tank containing highvapor tension rinse liquid and a vapor space overlying said tanks intowhich high vapor tension rinse vapor rises and condenses and the highvapor tension rinse distillate circulates into said rinse tank andcascades continuously from said rinse tank into said boil tank over theupper end of the common wall separating said tanks during operation ofsaid cleaning mode cycle, said cleaning mode cycle comprising the stepsof:(1) immersing soiled parts in said agitated admixture in said boiltank to remove soil therefrom, and (2) transferring said parts from saidboil tank into said vapor space overlying said tanks and rinsing same insaid high Vapor tension rinse vapors therein, andduring said shut downcycle of said process preventing losses of high vapor tension rinsevapors from said rinse tank comprising the microprocessor controlledstep of positioning a layer of said low vapor tension cleaner liquidover the surface of said high vapor tension rinse liquid in said rinsetank.
 2. A process in accordance with claim 1 wherein said low vaportension cleaner layer is formed by using a portion of said low vaportension cleaner liquid in said boil tank.
 3. A process in accordancewith claim 1 wherein said low vapor tension cleaner layer is formed bycascading a portion of said low vapor tension cleaner liquid over theupper end of said common wall separating said boil and rinse tanks.
 4. Aprocess in accordance with claim 1 wherein said low vapor tensioncleaner cover layer is established in position atop said high vaportension rinse liquid in said rinse tank by microprocessor controlledsteps comprising:(1) terminating agitation of the admixture of low vaportension cleaner and high vapor tension rinse liquids in said boil tankand forming a separated layer of low vapor tension cleaner liquidoverlying a layer of high vapor tension rinse liquid in the lowerportion of said boil tank, (2) terminating the agitation of the highvapor tension rinse liquid in said the rinse tank, (3) pumping highvapor tension rinse liquid from the bottom portion of said rinse tankinto the lower portion of said boil tank and directly into thestratified high vapor tension rinse liquid layer in said lower portionof said boil tank, (4) continuing the pumping of step (3) to cause thestratified layer of low vapor tension cleaner liquid overlying said highvapor tension rinse liquid to rise to the level of the upper end of saidcommon wall separating said boil and rinse tanks and to cascade intosaid rinse tank and to form a covering layer over said high vaportension rinse liquid, and (5) sensing the arrival of low vapor tensioncleaner liquid at the desired top level for said cover layer and bysignal to said microprocessor initiating de-energization of the pumpmeans to thereby stop pumping high vapor tension rinse liquid initiatedin step (3).
 5. A process in accordance with claim 1 includingmicroprocessor controlled steps for removing said low vapor tensioncleaner cover layer from its position atop the high vapor tension rinseliquid in said rinse tank during said shut-down cycle comprisingagitating the said low vapor tension cleaner and high vapor tensionrinse liquids in said boil tank and heating said admixture to boiling todistill high vapor tension rinse vapors into said vapor space,condensing said vapors, collecting said distillate and delivering saiddistillate into said rinse tank in sufficient quantity to raise thelevel of high vapor tension rinse liquid to thereby raise said low vaportension cleaner layer to the top of said common wall separating saidboil and rinse tanks and cascade the low vapor tension cleaner liquid insaid layer into said boil tank in its entirety and thereafter initiatingagitation of the high vapor tension rinse liquid in said rinse tank tothereby start up said cleaning mode cycle of said process.